This brick is used to phase external I²C components into the brick system. It contains two internal voltage sources 3.3V and 5V and an internal conversion between 3.3V and 5V I²C for the signal voltages. This can be used to complete three tasks. First of all, you can also work with brick components on the common I²C bus, which are only offered with 3.3V by the chip manufacturer. The other two functions are the possibility of integrating external sensors with 3.3V and also with 5V into the brick system via connecting wires. Of course, the 3.3 and/or 5V can also be used as a stable voltage source for small currents using a bridge.